public class Circle {
    private double radius;
    public Circle(){} 
    public Circle(double radius) {
        this.radius = radius;
    }
    public double getRadius(){
        return radius;
    } 
    public void showCircumference() {
        double circumference = 2 * Math.PI * radius;
        System.out.printf("圆的周长：%.2f\n", circumference);
    }
    public void showArea() {
        double area = Math.PI * radius * radius;
        System.out.printf("圆的面积：%.2f\n", area);
    }
    public static void main(String[] args) {
        Circle circle = new Circle(5.0); 
        circle.showCircumference();      
        circle.showArea();              
    }
}
